Question

(a)What is the commercial unit of electric energy? Express it in
terms of S.I unit of energy.
(b) An electric kettle consumes 1kW of electric power when
operated at 220V. Calculate the current drawn by the kettle. A fuse
wire of what rating must be used for it?

Answer 1

Answer:

Commercial unit of energy is kWh

Answer 2

ANSWER:--------

ANS 1.) THE COMMERCIAL UNIT OF ENERGY IS KILOWATT-HOUR.

NOW,RELATION BETWEEN KILOWATT-HOUR AND JOULE:

1KW-h =1KW FOR 1 HOUR

1KW-h =1000 WATTS FOR 1 HOUR------(1)

BUT WE KNOW THAT 1 WATT =

$\frac{1 \: joule}{1 \: second}$

SO WE CAN WRITE EQUATION 1 AS

1KW-h=1000

$\frac{joules}{seconds} for \: 1 \: hr$

1 HOUR=60×60 SECONDS

SO,1KW-h =1000 joules/seconds ×60×60 seconds

•°• 1KW-h =36,00,000 JOULES.

ANS 2.) POWER =1kwh =1000 w

V=220V

WE KNOW P=V×I

1000=220×I

I=4.54 A (approx.)

NOW,

P=v^2/R

So,

1000=(220)^2/R

R=48.4 ohm

THUS,WE CAN SAY HE MUST USE THE WIRE WHICH WOULD BE ABLE TO CARRY 4.54 A CURRENT.